It is well known that seats in certain work environments, such as driver seats for heavy transport vehicles, like trucks or buses, or in other operator stations, require them to be efficient, ergonomic, and comfortable, especially in the cases where the drivers or operators are exposed to long periods in a seated position. Accordingly, such seats must be adjustable to the user's needs.
Lumbar supports are of particular interest since several drivers or operators suffer from back pain. Very often lumbar pain can hinder greatly the accomplishments of their operator or driver functions.
Seats having inflatable balloons at the lumbar level harden the cushion by compressing foam which changes the comfort level of the cushion. In most cases, the balloons are located behind the foam. During inflation, the balloons push against the foam which is compressed and warped locally. The foam compresses itself mainly because it remains, independently of the change it is given by the balloon, integral to the structure of the back, which does not move during the adjustment of the seat.
International laid-open application nos. WO 98/58566 and WO 98/42234 describe different lumbar supports. In these two applications, the supports comprise independent devices that are designed to be added to a seat having its own structure. The adjustment of these devices along the height of the back is only a modulation of the overall shape of the back of the seat, and thus does not meet present requirements in the designs of lumbar supports for seats.
Another type of mechanism used in this field are mechanical adjustment devices for lumbar supports. Such mechanical adjustment devices are positioned behind the foam to accentuate the lumbar curve by pressing more or less on the back of the cushion. The foam of the cushion has an initial lumbar form that the mechanical device modifies by applying an additional pressure behind the cushion. As is the case for the adjustment system with balloons, the mechanical adjustment device has the effect of compressing the foam which hardens. Examples of such mechanical devices are described in international laid-open patent applications Nos. WO 97/30613, WO 98/53723, WO 01/70075, WO 02/01988 and WO 03/039300.
Other documents describe a complete suite of lumbar support adjustment systems, which act in several directions, including those transverse to the back, along the height of the back and laterally. By way of example, reference can be made to international laid-open application WO 99/55200 by AMERICAN COMPONENTS INC. which describes a device that can be added to a seat which already has a foam and support system. Consequently all of the above-mentioned patents do not provide for a maintenance of the comfort level that is initially provided by the foam cushion after various lumbar support adjustments.
The role of a good lumbar support is to relieve any stress on lumbar vertebrae by supporting a part of the weight of the body above the waist. This is accomplished by filling the empty space left between a flat back of a seat and the spine having its natural curvature. It is very important to localize the bump in the lumbar support with respect to the top part of the curvature of the lumbar vertebrae rather than with respect to the bottom of the back, since at the same time as filling the empty space, the lumbar support must maintain the upper back in a rest position while protecting it against shocks, for example due to chaotic road conditions.
However, the lumbar support looses its efficiency if it produces pressure points that are too excessive, which is the case of traditional lumbar supports or those described in the above-mentioned patent applications. Since the problem associated with most lumbar supports is related to the fact that the foam is fixed to a frame which is then compressed under the action of a lumbar support device, the solution is to design a frame or a cushion structure support that can adjust its shape and therefore help relieve stresses on the back.